Electrical measuring device



April 6, 1943. T. D. BARNES ELECTRICAL MEASURING DEVICE Filed Jan. 7,1942 0 pad INVENTOR 7770/7905 .50K/w25 /WTTORNEY WITNESS; @mi

Patented Apr. 6, 1943 UNITED STATES PATENT OFFICE ELECTRICAL MEASURIN GDEVICE of Pennsylvania Applica-tion January 7, i942, Serial No. 425,963

Claims.

This invention relates to electromotive devices, and it has particularrelation to electrical measuring devices having moving parts subject toundesired forces varying as functions of temperature.

In electromotive devices moving parts are employed which are providedwith suitable bearing means. For example, an induction Watthour meterincludes an armature structure which is mounted for rotation in suitabletop and bottom bearings. One of the best bottom bearings available 4isthat employing a steel ball. This bearing requires no lubrication. Inaccordance with the best modern practice, the top bearing of theinduction watthour meter is lubricated. The lubricants commonly7employed for this purpose have viscosities which vary as functions oftemperature.

Because of the variation in viscosity of the lubricant employed in thetop bearing of an induction Watthour meter, the lubricant develops adrag or retarding force which acts on the armature structure of themeter to oppose rotation thereof and this retarding force varies inmagnitude as a function of temperature. Because of this variation in theretarding force, the adjustment devices conventionally employed for theinduction Watthour meter are not suitable for compensating thisretarding force. Recently suitable compensating means for this purposehas been developed, and such means is disclosed in the copendingapplication of A. J. Petzinger, Serial No. 428,493, filed January 28,1942, and assigned to the Westinghouse Electric & Manufacturing Company.

The desirability of such compensation will be recognized when it isappreciated that the modern watthour meter often is subjected to asubstantial temperature variation. In modern practice many watthourmeters are placed outdoors and consequently are subject to atmospherictemperature variations. In such locations it is not uncommon for awatthour meter to be subjected to temperatures ranging from -20 C. to|50 C.

In accordance with this invention simple means are provided forcompensating an electromotive device such as an induction watthour meterfor errors introduced by the bearing lubricant employed therefor. Thiscompensation may take the form of a magnetic member for modifying thesymmetry of the magnetic circuits provided in the watthour meter forVoltage magnetic flux. The modilication in symmetry of the magneticcircuit is designed to provide an auxiliary force assisting in drivingthe armature structure of the meter. If the magnetic memer is formed ofa material having a substantial negative temperature coefficient ofpermeability it may be proportioned to produce an auxiliary forcevarying in magnitude with temperature sufciently to compensatesubstantially for the retarding force produced by the lubricant.

It is, therefore, an object of the invention to provide an electromotivedevice having improved means for compensating the device againsttemperature responsive errors.

It is a further object of the invention to provide a watthour meterhaving a magnetic member formed of a material having a substantialtemperature coefficient of permeability positioned to modify thesymmetry of the magnetic path offered to voltage magnetic flux andproportioned to produce an auxiliary force compensating for the effectsof the retarding force produced by meter bearing lubricant.

It -is another object of the invention to provide an induction watthourmeter having a magnetic member formed of material having a substantialnegative temperature coe'cient of permeability positioned to modify thesymmetry of the magnetic paths oiiered to voltage magnetic ux in orderto apply an auxiliary force to the armature structure of the meter andhaving a light load adjuster operable for adjusting the performance ofthe meter under light load conditions.

Other objects of the invention will be apparent from the followingdescription taken in conjunction with the accompanying drawing, inwhich:

Figure l is a view in front elevation of an induction watthour meterembodying the invention;

Fig. 2 is a View in cross section with parts broken away taken along theline II--II of Fig. 1;

Fig. 3 is a graphical representation illustrating the characteristics ofthe watthour meter shown in Figs. 1 and 2; and

Fig. 4 is a graphical representation showing the characteristics ofmaterial employed in the watthour meter of Figs. 1 and 2.

Referring to the drawing, Figure l shows a watthour meter I having amagnetic core 2. This magnetic core 2 includes a voltage pole 3 andcurrent poles 5 and 'l which are spaced to define an air gap. Anelectroconductive armature structure such as a copper or an aluminumdisk Q is mounted for rotation in this air gap. To this end, the disl; 9may be attached to a shaft II which is provided with a top bearing I3and a bottom bearing I5. Either or both of These bearings may be of thelubricated type. In the specific modification shown in Fig. 1, thebearing i5 is formed of a steel ball Il which is positioned between asapphire cup I9 carried by the shaft II and a sapphire cup 2i which isattached to a fixed part of the watthour meter. This construction is oneof the best available for bottom bearings and operates satisfactorily ina dry or unlubricated condition. The tcp bearing I3 may be inthe form ofa collar 23 carried by the shaft i! and having an orifice for receivinga pin which is attached to a stationary part of the watthour meter.

In accordance with conventional practice, the top bearing I3 islubricated by means of a suitable lubricant. It has been found thatpetrolatum constitutes a satisfactory lubricant for this bearing. Thelubricant serves not only to decrease wear of the bearing surfaces butit also acts as a cushion to decrease noise and vibration or chatter ofthe bearing. Suitable constructions for the bearings I3 and i5 are shownin detail in the Paszkowski Patent 1,728,507.

In order to energize the watthour meter i a voltage winding 2l ispositioned about the voltage pole 3 and current windings 2Q and 3i arepositioned about the current poles 5 and 'I'. As well understood in theart, when the windings 2l, 253 and 3l are energized in accordance withthe voltage and current of an electrical circuit, a shifting magneticeld is established in the air gap containing the disk 9. This shiftingmagnetic field is dependent upon the energy flowing in the associatedelectrical circuit and serves to apply a torque to the disk 9 forrotating the disk. A permanent magnet (not shown) conventionally isemployed for damping rotation of the disk 9. It will be assumed that thedirection of the shifting magnetic field is such that a mark 33 on theedge of the disk 9 moves in the direction of the arrow 35.

In order to adjust the watthour meter i for satisfactory operation underlight load conditions, an electroconductive loop or plate 3l' ispositioned for adjustment across the pole face of the voltage pole 3. Byproper adjustment of the plate 3l, the performance of the watthour meterl under light load conditions may be adjusted as desired.

It will be observed that the magnetic core 2 includes a pair of arms 3dand il which terminate adjacent opposite sides of the voltage pole 3near the pole face thereof. These arms 39 and Si serve to divert asubstantial proportion of the voltage nux produced by the voltagewinding il away from the armature structure or disk t, and they increasesub-stantially the inductance of the voltage winding El. It will beobserved further that the arms 3? and Si establish magnetic paths whichare symmetric with reference to the voltage pole 3. This symmetry is forthe purpose of assuring a uniform distribution of the voltage magneticflux in the neighborhood of the voltage pole face.

It is believed that the operation of the structure thus far described isapparent from the loregoing description. The structure of the watthourmeter i thus far described well known in the art. If desired, anoverioad shunt 043 may be positioned between the current poles 5 and lfor diverting current magnetic flux away from the disk 9. As wellunderstood in the art, this shunt is designed to saturate or operatewith decreasing magnetic permeability above a predetermined value ofcurrent passing through the windings 2G and 3l in order to improve theaccuracy of the watthour meter operation.

As previously pointed out, the effect of lubricant employed in one orboth bearings of the watthour meter is to apply a drag or retardingforce to the disk Q. This retarding force is not constant but varies asa function of temperature. The effect of the ret-arding force on theoperation of the watthour meter may be understood more clearly byreference to Fig. 3.

In Fig. 3, curves are shown representing the performance of the watthourmeter I. These curves represent percent error in registration of thewatthour meter piotted as ordinates against the load measured by thewatthour meter as abscissae. The ideal characteristic of the watthourmeter I is represented by a curve A which exhibits no error at any valueof the load measured by the watthour meter.

If the watthour meter I is adjusted to approximate as close as possiblethe characteristic represented by the curve A, a drop in the temperatureof the watthour meter will result in a new characteristic curve B. Itwill be observed that the characteristic curve B droops appreciably inthe light load region. This drocp indicates that the watthour meter i isrunning toc slowly and is registering incorrectly. The drcop is causedby the increase in retarding force applied to the disk 9 by thelubricant for the bearing I3. As previously pointed out, this retardingforce increases substantially with a decrease in temperature of thewatthour meter. Since the retarding force represents a small percentageof the higher load values measured by the watthour meter I, the effectthereof on the accuracy of the watthour meter is insignificant forhigher load values. At light load values, however, the retarding forceis an appreciable percentage of the load measured 'by the watthour meterand results in a substantial error in the performance thereof.

In order to compensate the watthour meter i for errors introduced by theaforesaid retarding force, it is desirable that an auxiliary force beapplied to the disk 9 which is equal and opposite to the retardingforce. This auxiliary force is represented by a curve C shown by adotted line in Fig. 3. It will be observed that the curve Csubstantially balances the droop in the curve B and provides a resultantperformance of the watthour meter I which is repre-- sentedsubstantially -by the curve A.

Production of the auxiliary force represented by the curve C is effectedby positioning a magnetic member i5 in one of the magnetic pathscompleted by the arms 38 and ril. This magnetic member modies thesymmetry of the magnetic paths established by the arms 39 and Il! andresults in a non-uniform distribution of voltage flux in the voltagepole adjacent the voltage pole face. The effect of this non-uniformdistribution of magnetic ux is to apply an auxiliary force to the disk9. Depending upon the particular effect desired, the magnetic member 45may be positioned on either side of the voltage pole 3' to produce anauxiliary force urging the disk i5 in either direction. In the specificembodiment herein set forth, the magnetic member 45 isfpositionedbetween the voltage pole 3 and the arm 4I to produce an auxiliary forceurging the disk d in the4 direction of the arrow B. Consequently, theauxiliary force tends to compensate for the retarding force produced bythe drag of the lubricant in the bearing I3.

To provide complete compensation for the retarding force, the auxiliaryforce produced by the magnetic member 45 should vary as a function oitemperature. This variation may be effected by forming the magneticmember 45 of a material having a substantial temperature coeiiicient ofmagnetic permeability. By forming the magnetie member 1&5 of a materialhaving a substantial negative temperature coeiiicient of permeability,the auxiliary force increases substantially as the temperature of themagnetic member decreases. By properly proportioning the magneticmember, the auxiliary force varies in magnitude with temperaturesufliciently to compensate substantially for the retarding forceproduced by the drag cf the lubricant in the bearing I3. Magneticmaterials having substantial negative temperature coefficients ofpermeability are well known in the art. These materials comprisegenerally an iron alloy containing approximately of nickel which issuitably heat treated.

Nickel-copper alloys also are employed for this purpose. Thecharacteristics of the material ernployed for the magnetic member may bedepicted by a curve as shown in Fig. 4, wherein ordinates representpermeability and abscissae represent temperature of the material. Itwill be observed that as the temperature drops from C. above zero to 20C. below zero, the permeability of the material increases substantially.

The magnetic member 135 conveniently may be formed of a strip of thedesired material which is wedged between the arm 4| and the voltage pole3. Other means for mounting the material in position and other shapesthereof may be employed as desired.

It is believed that the operation o1" the invention is clear from theabove discussion.` The magnetic member 45 is proportioned to provide anauxiliary force urging the disk 9 in the direction of the arrow 35 whichvaries in magnitude with the temperature of the magnetic membersubstantially at the same rate as the corresponding variation in theretarding force produced by the drag oi the lubricant in the bearing I3.Ii the light load adjustment plate 37 is then adjusted to provide thedesired light load characteristics at a predetermined temperature, thesame characteristics will be obtained over a substantial range oftemperature variation.

By following the teachings of this invention an electromotive device,such as a watthour meter, may be ccmpensated substantially for errors,which vary with the temperature thereof. Althrough the invention hasbeen described with reference to certain specic embodiments thereof,numerous modifications are possible. Therefore, the invention is to berestricted only by the appended claims when interpreted in View of theprior art.

I claim as my invention:

1. In a measuring device, a magnetic structure having a plurality ofmagnetic pole elements dening an air gap, means effective when energizedfor directing magnetic flux through said pole elements tc establish ashitting magnetic eld in said air gap, an electroconductive armaturestructure positioned in said air gap, bearing means mounting saidelectroconductive armature structure for movement in said air gap underthe inuence of said shifting magnetic iield, said measuring deviceincluding means intrcducing a force component varying as a function oftemperature and acting to modify the correct movement of said armaturestructure, and means compensating said measuring device for errorsintroduced therein by said force component, said compensating meansincluding a magnetic member cooperating with one of said pole elementsand positioned asymmetrically with respect to the pole face of said oneof said pole elements to vary the i'lux distribution in said pole facein an asymmetric pattern for producing an auxiliary shifting magneticfield in said air gap to oppose the eiiect of said force component onsaid armature structure, said magnetic member having a substantialtemperature coefficient oi permeability for varying said auxiliaryshifting magnetic field with temperature suiiciently to compensate saidforce component over a substantial range of temperature variation.

2. In an electrical watthour meter for measuring energy flowing in anelectrical circuit, a magnetic core having a voltage pole element andcurrent pole elements spaced to define an air gap, means for producingin said air gap a shifting magnetic eld, said means including meanseffec tive when suitably energized for producing voltage and currentmagnetic iiuxes in said pole elements, an electroconductive armaturestructure, means mounting said armature structure for r0- tation in saidair gap under the influence of said shifting magnetic held, saidmounting means including means opposing rotation of said armaturestructure with a retarding force which increases for a decrease intemperature, and compensating means for compensating errors introducedin said watt-hour meter by said retarding force, said compensating meanscomprising light load adjusting means ior adjusting the torque appliedvto said armature structure at a light loading of said watthour meter,and a magnetic member positioned adjacent the pole face of said voltagepole element for diverting a portion of the magnetic ux flowing in saidvoltage pole element away from said armature structure, said magneticmember being positioned asymmetrically relative to the pole face of saidvoltage pole to produce an auxiliary shifting magnetic iield in said airgap acting on said armature structure in opposition to said retardingforce, and said magnetic member having a substantial negativetemperature coeicient of permeability, whereby said auxiliary shiftingmagnetic iield decreases for an increase in temperature of said watthourmeter.

3. In an electrical watthour meter for measuring energy flowing in anelectrical circuit, a magnetic core having a voltage pole element andcurrent pole elements spaced to define an air gap, means for producingin said air gap a shifting magnetic neid, said means including meanseffective when suitably energized for producing voltage and currentmagnetic iiuxes in said pole elements, an electroconductive armaturestructure, means mounting said armature structure for rotation in saidair gap under the infiuence of said shifting magnetic eld, said magneticcore including bypass means symmetrically disposed relative to the poleface of said voltage pole element in the direction oi movement of saidarmature structure relative thereto for diverting a portion of thevoltage magnetic iiux away from said armature structure, said mountingmeans including means opposing rotation of said armature structure witha retarding force which increases for a decrease in temperature, andcompensating means for compensating errors introduced in said watthourmeter by said retarding force, said compensating means comprising lightload adjusting means for adjustingrthe torque applied lto said armaturestructure at a light loadingv of said Watthour meter, and a magneticmember positioned in a magnetic path deiined by said bypass meansasymmetrically relative to the pole face of said voltage pole elementfor applying an auxiliary force to said armature structure acting inoppositicn to said retarding force, said magnetic member having asubstantial negative temperature coeiiicient of permeability, and saidmagnetic member being proportioned to effect a temperature responsivevariation of said auxiliary force substantially similar to that of saidretarding force.

4i. In an electrical Watthour meter for measuring energy fiowing in anelectrical circuit, an electroconductive armature structure, meansmounting said electroconductive armature structure for rotation in saidair gap, said mounting means including means opposing rotation of saidarmature structure With a retarding force which increases for a decreasein temperature thereof, means associated with said magnetic core forproducing in said air gap a shifting magnetic eld operating to rotatesaid armature, said magnetic core comprising a voltage pole elementhaving a pole face positioned adjacent said armature structure, and apair of magnetic arms terminating adjacent opposite sides of saidvoltage pole element for establishing magnetic paths diverting voltagemagnetic flux flowing therethrough away from said armature structure, amagnetic member having a negative temperature coeicient of permeabilitypositioned in one of said magnetic paths for controlling the symmetrythereof relative to said voltage pole face, said magnetic member beingproportioned for producing a temperature responsive auxiliary shiftingmagnetic field in said air gap to apply to said armature structure anauxiliary force opposing said retarding force over a substantial rangeof temperature variation, and light load adjusting means for adjustingthe torque applied to said armature structure at a light loading of saidWatthour meter.

5. In an electrical watthour meter for measuring energy flowing in an`electrical circuit, a magnetic core having a voltage pole element andcurrent pole elements positioned with their pole faces defining an airgap, said magnetic core being designed to provide a pair ofsymmetrically arranged magnetic paths terminating adjacent oppositesides of the pole face of said voltage pole element for diverting aportion of the voltage magnetic flux ovving in said voltage pole elementaway from said air gap, means for producing in said air gap a shiftingmagnetic eld moving across the pole face of said voltage pole elementIfrom one of said sides towards the other of said sides and dependent onthe value of the energy to be measured, an electroconductive armaturestructure, means mounting said armature structure in said air gap forrotation under the influence of said shifting magnetic field, saidmounting means including means opposing rotation of said armaturestructure with a retarding force which increases for a decrease in thetemperature oi said watthour meter, and means compensating said Watthourmeter for .errors introduced by said retarding force, said compensatingmeans comprising a magnetic member having a negative temperaturecoeiiicient of permeability positioned in one of said magnetic paths formodifying the symmetry of said magnetic paths relative to the pole faceof said voltage pole element, the modification of the symmetry of saidmagnetic paths being designed to produce a shifting magnetic fieldcomponent acting in opposition to, and substantially balancing saidretarding force over a substantial range of temperature variation, andlight load adjusting means for adjusting the torque applied to saidarmature structure at a light loading of said watthour meter.

THOMAS D. BARNES.

